The objectives of the present proposal are to elucidate the ultrastructural and functional features of the mitotic apparatus (MA) in normal and neoplastic cells. Experiments are designed to gain new insight into the control of assembly and disassembly of the MA. Specifically our studies are aimed at: (a) the structure and function of the Kinetochore, (b) further studies of the centriole, (c) relationship between nuclear enuelone and Kinetochore and (d) mitotic events in mammalian cell hybrids. For the current year we set the following goals: application of tubulin antibody to the localization of tubulin and microtubules in normal and transformed cells in culture; (2) development of an in vitro microtubule assembly system using human chromosomes and centrioles as nucleating sites for the assembly of tubulin from exogenous sources; (3) investigation of factors which control microtubule assembly in mammalian fibroblasts in culture. BIBLIOGRAPHIC REFERENCES: Brinkley, B.R. and Walter N. Hittelman. 1975. Ultrastructure of Mammalian Chromosome Aberrations. Int. Rev. Cytol. 42: 49-101. Fuller, Gerald M., B. R. Brinkley, and J. Mark Boughter. 1975. Immunofluorescence of Mitotic Spindles Using Monospecific Antibody Against Bovine Brain Tubulin. Science, 187: 948-950.